Sealing subterranean zones

ABSTRACT

The present invention provides improved compositions and methods of using the compositions for sealing subterranean zones. One composition of the invention is comprised of water, an aqueous rubber latex, an organophilic clay, sodium carbonate, an epoxy resin and a hardening agent for said epoxy resin.

[0001] This Application is a Continuation-In-Part of application Ser.No. 09/244,820 filed on Feb. 4, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to improved compositions forsealing subterranean zones and methods of utilizing the compositions.

[0004] 2. Description of the Prior Art

[0005] In the drilling of oil and gas wells using the rotary drillingmethod, drilling fluid is circulated through the drill string and drillbit and then back to the surface by way of the well bore being drilled.The drilling fluid maintains hydrostatic pressure on the subterraneanzones through which the well bore is drilled and circulates cuttings outof the well bore. During such drilling, subterranean vugs, fractures andother highly permeable zones are often encountered whereby the drillingfluid circulation is lost into the zones and drilling operations must beterminated while remedial steps are taken. Also, when a subterraneanzone is penetrated containing fluids under pressure which exceeds thehydrostatic pressure exerted on the zone by the drilling fluid,formation fluid crossflows and/or underground blow-outs can and often dooccur.

[0006] Heretofore, a variety of compositions have been developed andused for combating lost circulation, crossflow and underground blow-outproblems. However, such compositions have often been unsuccessful due todelayed and inadequate viscosity development by the compositions. Forexample, a variety of compositions containing hydraulic cement or thelike have been used in attempts to stop lost circulation. The lostcirculation is usually the result of encountering weak subterraneanzones that contain natural fractures and/or are fractured by drillingfluid pressures and rapidly break down. When a cement or other slowsetting composition is squeezed into the zone, the delay in developinghigh viscosity allows the sealing composition to be diluted anddisplaced into the zone whereby it bypasses the fractures and vugscausing the lost circulation. The same type of problem often occurs whencrosslinked hydrated gels and other similar sealing compositions areutilized.

[0007] Thus, there are needs for improved compositions and methods ofsealing subterranean zones using the compositions whereby thecompositions develop ultra high viscosities in a few seconds or minutesand thereafter harden into firm but resilient sealing masses.

SUMMARY OF THE INVENTION

[0008] Improved compositions and methods of using the composition forsealing subterranean zones are provided which overcome the deficienciesof the prior art and meet the needs described above. The sealingcompositions and methods are particularly suitable for sealingsubterranean zones containing drilling fluids formed of oil, watercontaining divalent cations and/or water-in-oil emulsions, known in theart as inverted emulsions.

[0009] A first sealing composition of this invention for sealing zonescontaining oil or water based drilling fluids is basically comprised ofwater, an aqueous rubber latex, an organophilic clay, sodium carbonate,an epoxy resin and a hardening agent for the epoxy resin. Thecomposition can also include one or more latex stabilizers, dispersingagents, biopolymers, defoaming agents, foaming agents, emulsionbreakers, fillers, rubber vulcanizing agents and the like.

[0010] A second sealing composition of this invention for sealingsubterranean zones containing oil or water based drilling fluids isbasically comprised of an aqueous rubber latex, a latex stabilizingsurfactant, an epoxy resin and a hardening agent for the epoxy resin.

[0011] A third inventive sealing composition for sealing subterraneanzones containing water based drilling fluids is basically comprised of awater swellable clay, a silane coupling agent, an epoxy resin and ahardening agent.

[0012] When the first and second sealing compositions described abovecontact oil, water containing divalent cations or oil-water emulsions ina well bore, the rubber latex is destabilized whereby the rubber isprecipitated thereby forming the sealing composition into a viscousmass. When the sealing composition includes an organophilic clay, theorganophilic clay simultaneously reacts with the oil to instantly forman ultra-high viscosity rubbery mass. The third sealing compositiondescribed above includes a water swellable clay which forms thecomposition into a viscous mass when it contacts water. The viscousmasses formed by the sealing compositions remain in the zones to besealed until the epoxy resin in the sealing compositions is hardened bythe hardening agent which forms the compositions into firm but resilientsealing masses which retain their shape, have compressive strength andeffectively seal the subterranean zones.

[0013] The methods of this invention basically comprise the steps ofpreparing a sealing composition of this invention, introducing thesealing composition into a subterranean zone to be sealed and allowingthe sealing composition to form a firm but resilient sealing mass in thesubterranean zone.

[0014] It is, therefore, a general object of the present invention toprovide improved compositions for sealing subterranean zones and methodsof using the compositions.

[0015] Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] As mentioned above, in the drilling of wells, subterranean zonesare often encountered which contain high incidences of natural vugs andfractures. As a result, drilling fluid circulation is often lost whichrequires the termination of the drilling and the implementation ofremedial procedures which are often of long duration and high cost. Suchremedial procedures have heretofore involved the placement of hardenablecompositions such as Portland cement compositions or crosslinked stiffgels and the like in the lost circulation zone. However, as mentionedabove, because such compositions require considerable time to harden orgel, successful plugging of the zone often does not take place. Inaddition to drilling fluid loss circulation zones, zones containingpressurized fluids can be encountered which cause gas, oil and/or watercrossflows that dilute and wash away sealing compositions. Also,underground blow-outs at low to high formation fluid flow rates can takeplace.

[0017] The present invention provides improved compositions for sealingsubterranean zones and terminating the loss of drilling fluid,crossflows and/or underground blow-outs. The compositions areparticularly suitable for use in wells containing oil, water containingdivalent cations and/or water-in-oil emulsions. When a composition ofthis invention contacts oil or water containing divalent cations in thewell bore, it instantly forms a viscous sealing mass. As the viscoussealing mass is displaced through the well bore, it enters and sealsvugs, fractures and other highly permeable zones through which fluid islost. Upon entering such zones, the viscous sealing composition isretained in the zones long enough for the epoxy resin therein to hardenand form a firm but resilient sealing mass which retains it shape, hascompressive strength and effectively seals the zones.

[0018] The sealing compositions of this invention are self diverting andplug multiple weak zones in a single well treatment. When a wellcontains a crossflow or underground blow-out, the sealing compositionsplug all the lower pressure weak zones penetrated by the well bore andas the pressure in the well bore is increased, the crossflow or blow-outzone is also plugged. The resulting sealed well bore achieved by thesealing compositions of this invention can hold higher drilling fluidweights and the sealing compositions produce a wedging effect in pluggedfractures that increases the integrity of the entire sealed formation orzone.

[0019] A first sealing composition of the present invention is basicallycomprised of water, an aqueous rubber latex, an organophilic clay,sodium carbonate, an epoxy resin and a hardening agent for the epoxyresin. The aqueous rubber latex present in the composition is caused todestabilize by oil or water containing electrolytes such as calciumchloride in the well bore whereby the rubber is precipitated. Theorganophilic clay simultaneously reacts with oil in the well bore toform a high viscosity rubbery sealing mass. The sodium carbonate in thecomposition functions to stabilize the rubber latex and preventprecipitation when the latex is mixed with water which contains calciumchloride and the like during the preparation of the composition. Sodiumhydroxide can also be added to the composition to prevent precipitationof the latex if the water used to form the composition containsmagnesium compounds or other similar latex destabilizing compounds.

[0020] The epoxy resin in the compositions is caused to harden by thehardening agent therein whereby the initially formed high viscosityrubbery sealing mass is converted into a firm but resilient sealing masswhich has compressive strength and retains its shape in a sealed zone.

[0021] The water in the sealing composition which is in addition to thewater contained in the aqueous latex is included in the composition tomake it pumpable. The water can be from any source provided it does notcontain the above mentioned compounds that adversely affect the rubberlatex or other components in the composition. However, fresh water ispreferred. Generally, the additional water is present in an amount inthe range of from about 6% to about 50% by weight of the composition,more preferably in a range of from about 30% to about 42%.

[0022] A second sealing composition which is similar to the abovedescribed composition is basically comprised of an aqueous rubber latex,a latex stabilizing surfactant, an epoxy resin and a hardening agent forthe epoxy resin. The aqueous rubber latex is caused to destabilize byoil or water containing electrolytes in the well bore whereby the rubberis precipitated and a viscous sealing mass is formed. As describedabove, the viscous sealing mass enters and seals vugs, fractures andother highly permeable zones and is retained in the zones long enoughfor the epoxy resin therein to harden. The resulting sealing massretains its shape, has compressive strength and effectively seals andstrengthens the zones.

[0023] A third inventive sealing composition is basically comprised of awater swellable clay, a silane coupling agent, an epoxy resin and ahardening agent for the epoxy resin. When the water swellable claycontacts water, it swells and forms the sealing composition into aviscous mass which enters and seals vugs, fractures and other highlypermeable zones and is retained in the zones long enough for the epoxyresin therein to harden. The resulting sealing mass retains its shape,has compressive strength and effectively seals and strengthens thezones.

[0024] A variety of well known rubber materials can be utilized inaccordance with the present invention. Such materials are commerciallyavailable in aqueous latex form, i.e., aqueous dispersions or emulsions.For example, natural rubber (cis-1,4-polyisoprene) and most of itsmodified types can be utilized. Synthetic polymers of various types canalso be used including styrene/butadiene rubber, cis-1,4-polybutadienerubber and blends thereof with natural rubber or styrene/butadienerubber, high styrene resin, butyl rubber, ethylene/propylene rubbers,neoprene rubber, nitrile rubber, cis-1,4-polyisoprene rubber, siliconerubber, chlorosulfonated rubber, polyethylene rubber, epichlorohydrinrubber, fluorocarbon rubber, fluorosilicone rubber, polyurethane rubber,polyacrylic rubber and polysulfide rubber.

[0025] Of the various latexes which can be utilized, those prepared byemulsion polymerization processes are preferred. A particularlypreferred latex for use in accordance with this invention is astyrene/butadiene copolymer latex emulsion prepared by emulsionpolymerization. The aqueous phase of the emulsion is an aqueouscolloidal dispersion of the styrene/butadiene copolymer. The latexdispersion usually includes water in an amount in the range of fromabout 40% to about 70% by weight of the latex, and in addition to thedispersed styrene/butadiene particles, the latex often includes smallquantities of an emulsifier, polymerization catalysts, chain modifyingagents and the like. The weight ratio of styrene to butadiene in thelatex can range from about 10%:90% to about 90%:10%.

[0026] It is understood that styrene/butadiene latexes are oftencommercially produced as terpolymer latexes which include up to about 3%by weight of a third monomer to assist in stabilizing the latexemulsions. The third monomer, when present, generally is anionic incharacter and includes a carboxylate, sulfate or sulfonate group. Othergroups that may be present on the third monomer include phosphates,phosphonates or phenolics. Non-ionic groups which exhibit steariceffects and which contain long ethoxylate or hydrocarbon tails can alsobe present.

[0027] A particularly suitable styrene/butadiene aqueous latex for usein accordance with the present invention has a styrene/butadiene weightratio of about 25%:75%, and the styrene/butadiene copolymer is suspendedin a 50% by weight aqueous emulsion. A latex of this type is availablefrom Halliburton Energy Services of Duncan, Okla. under the tradedesignation “LATEX 2000™.”

[0028] When used in the first sealing composition described above whichalso includes an organophilic clay, sodium carbonate, an epoxy resin anda hardening agent, the aqueous latex is included in the composition inan amount in the range of from about 8% to about 17% by weight of thecomposition, more preferably in an amount of from about 10% to about12%.

[0029] When used in the second sealing composition described above whichalso includes a latex stabilizing surfactant, an epoxy resin and ahardening agent, the aqueous latex is included in the composition in anamount in the range of from 30% to about 70% by weight of thecomposition, more preferably in an amount of from about 40% to about50%.

[0030] While a variety of organophilic clays can be utilized, an alkylquaternary ammonium bentonite clay is preferred. A particularly suitablealkyl quaternary ammonium bentonite clay for use in accordance with thisinvention is commercially available from Southern Products, Inc. ofGonzales, Tex. under the tradename “CLAYTONE-II™.” The organophilic clayis generally present in the first sealing composition described above inan amount in the range of from about 13% to about 22% by weight of thecompositions, more preferably from about 16% to about 19%.

[0031] The sodium carbonate which functions as a buffer and preventsdestabilization of the rubber latex due to contact with calcium and thelike in the mixing water is generally present in the first sealingcomposition described above in an amount in the range of from about 2.7%to about 4.4% by weight of the compositions, more preferably from 3.3%to about 3.7%.

[0032] The compositions of this invention can include various epoxyresins. Preferred epoxy resins are those selected from the condensationproducts of epichlorohydrin and bisphenol A. A particularly suitablesuch resin is commercially available from the Shell Chemical Companyunder the trade designation “EPON®RESIN 828.” This epoxy resin has amolecular weight of about 340 and a one gram equivalent of epoxide perabout 180 to about 195 grams of resin.

[0033] For ease of mixing, the epoxy resin utilized in the first andsecond sealing compositions described above can be pre-dispersed in anon-ionic aqueous fluid. A non-ionic aqueous dispersion of the epoxyresin, i.e., the above described condensation product of epichlorohydrinand bisphenol A, is commercially available from the Shell ChemicalCompany under the trade designation “EPI-REZ®-3510-W-60.” Anothernon-ionic aqueous dispersion of an epoxy resin comprised of acondensation product of epichlorohydrin and bisphenol A having a highermolecular weight than the epoxy resin described above is alsocommercially available from the Shell Chemical Company under the tradedesignation “EPI-REZ®-3522-W-60.” Yet another non-ionic aqueousdispersion of an epoxy resin suitable for use in accordance with thepresent invention includes an epoxidized bisphenol A novolac resin whichhas a one gram equivalent of epoxide per about 205 grams of resin. Thisnon-ionic aqueous dispersion of epoxy resin is commercially availablefrom the Shell Chemical Company under the trade designation“EPI-REZ®-5003-W-55.”

[0034] Of the foregoing non-ionic aqueous dispersions of epoxy resin,the aqueous dispersion of the condensation product of epichlorohydrinand bisphenol A having a molecular weight of about 340 and a one gramequivalent of epoxide per about 180 to about 195 grams of resin is themost preferred.

[0035] The epoxy resin utilized is included in the sealing compositionsof this invention in an amount in the range of from about 30% to about70% by weight of the compositions, most preferably in an amount of about40% to about 50%.

[0036] A solvent comprised of one or more aromatic hydrocarbons or a lowviscosity epoxide containing liquid or a mixture of such epoxidecontaining liquids can be utilized to modify the viscosity of the epoxyresin used, e.g., the above described Shell “EPON®RESIN 828,” and to addflexibility and resiliency to the epoxy containing sealing compositionafter hardening. A particularly suitable solvent which is presentlypreferred is comprised of a mixture of hydrocarbons containing fromabout 50% to about 99% of one or more aromatic hydrocarbons by weight ofthe solvent. Such a preferred solvent is commercially available underthe tradename “CYCLO SOL 63™” from Shell Chemical Co. of Houston, Tex.An epichlorohydrin/bisphenol A condensation epoxy resin which has beenmodified with an aromatic solvent and is suitable for use in the abovedescribed sealing compositions is commercially available from the ShellChemical Company under the trade designation “EPSEAL RE®.”

[0037] When an aromatic solvent or an epoxide containing liquid ormixture of such liquids is included in a sealing composition of thisinvention to modify the viscosity of an epoxy resin therein, the solventor epoxide containing liquid or mixture is generally present in anamount in the range of from about 20% to about 40% by weight of theepoxy resin in the sealing composition. An epoxide containing liquid ora mixture of such liquids can also be utilized as the only epoxidesource in a sealing composition of this invention.

[0038] While various epoxide containing liquids can be used, preferredsuch liquids are the diglycidyl ether of 1,4-butanediol, the diglycidylether of neopentyl glycol and the diglycidyl ether ofcyclohexanedimethanol. A suitable epoxide containing liquid comprised ofthe diglycidyl ether of 1,4-butanediol is commercially available fromthe Shell Chemical Company under the trade name “HELOXY®67.” Thisepoxide containing liquid has a viscosity at 25° C. in the range of fromabout 13 to about 18 centipoises, a molecular weight of 202 and a onegram equivalent of epoxide per about 120 to about 130 grams of theliquid. A suitable diglycidyl ether of neopentylglycol is commerciallyavailable from Shell Chemical Company under the trade name “HELOXY®68.”This epoxide containing liquid has a viscosity at 25° C. in the range offrom about 13 to about 18 centipoises, a molecular weight of 216 and aone gram equivalent of epoxide per about 130 to about 140 grams of theliquid. A suitable diglycidyl ether of cyclohexanedimethanol iscommercially available from Shell Chemical Company under the trade name“HELOXY®107.” This epoxide containing liquid has a viscosity at 25° C.in the range of from about 55 to about 75 centipoises, a molecularweight of 256 and a one gram equivalent of epoxide per about 155 toabout 165 grams of the liquid.

[0039] When an epoxide containing liquid or mixture is utilized as theonly epoxide source in a sealing composition of this invention, theepoxide containing liquid or mixture is generally present in an amountin the range of from about 40% to about 50% by weight of the sealingcomposition.

[0040] A variety of hardening agents, including, but not limited to,aliphatic amines, aliphatic tertiary amines, aromatic amines,cycloaliphatic amines, heterocyclic amines, amidoamines, polyamides,polyethylamines and carboxylic acid anhydrides can be utilized in thecompositions of this invention containing the above described epoxyresins. Of these, aliphatic amines, aromatic amines and carboxylic acidanhydrides are the most suitable.

[0041] Examples of aliphatic and aromatic amine hardening agents aretriethylenetetraamine, ethylenediamine, N-cocoalkyltrimethylenediamine,isophoronediamine, diethyltoluenediamine, andtris(dimethylaminomethylphenol). Examples of suitable carboxylic acidanhydrides are methyltetrahydrophthalic anhydride, hexahydrophthalicanhydride, maleic anhydride, polyazelaic polyanhydride and phthalicanhydride. Of these, triethylenetetraamine, ethylenediamine,N-cocoalkyltrimethylenediamine, isophoronediamine, diethyltoluenediamineand tris(dimethylaminomethylphenol) are preferred, withisophoronediamine, diethyltoluenediamine andtris(dimethylaminomethylphenol) being the most preferred.

[0042] The hardening agent or agents utilized are generally included inthe sealing compositions of this invention in an amount in the range offrom about 5% to about 30% by weight of the compositions.

[0043] Another component which can optionally be included in the sealingcompositions of this invention is a polymer which hydrates with waterand adds viscosity to the compositions to help maintain the solidstherein in suspension without adversely affecting the sealingcompositions such as by prematurely destabilizing the rubber latex. Thepolymer is preferably a biopolymer which is not degraded bymicroorganisms such as bacteria. A particularly preferred biopolymer foruse in accordance with this invention which does not adversely affectthe sealing compositions is welan gum. When used, the welan gum isincluded in the sealing compositions in an amount in the range of fromabout 0.1% to about 0.2% by weight of the compositions.

[0044] In order to facilitate the dispersal of solids in thecompositions, a dispersing agent can optionally be included therein.While a variety of dispersing surfactants can be used, preferreddispersing surfactants are the condensation reaction product of acetone,formaldehyde and sodium sulfite, the condensation reaction product ofsodium naphthalene sulfonate and formaldehyde andsodium-N-methyl-N-oleyltaurine mixed with sulfite liquor. Of these, thecondensation reaction product of acetone, formaldehyde and sodiumsulfite is most preferred. When used, the dispersing agent is includedin the compositions of this invention in an amount in the range of fromabout 0.35% to about 0.55% by weight of the compositions, morepreferably from about 0.4% to about 0.47%.

[0045] Another additive which can optionally be utilized is a defoamingagent which prevents foaming during mixing and pumping of the sealingcompositions. Because the aqueous rubber latex includes surfactants foremulsifying the latex which also function as foaming agents, a largebubble, unstable foam can be produced when the rubber latex is mixedwith water and the other components of the sealing compositions. Thedefoaming agent can comprise any of the compounds well known for suchcapabilities such as the polyol silicon compounds. A preferred suchdefoaming agent is polydimethylsiloxane which is commercially availablefrom Halliburton Energy Services of Duncan, Okla., under the tradedesignation “D-AIR™3.” When used, the defoaming agent is generallyincluded in the sealing compositions in an amount in the range of fromabout 0.4% to about 1.8% by weight of the compositions, more preferablyfrom about 0.8% to about 1.2%.

[0046] In order to prevent the aqueous latex from prematurelycoagulating and increasing the viscosities of the sealing compositionsof this invention due to contact with coagulation causing compounds inthe water used or other source, an effective amount of a latexstabilizing surfactant can be included in the compositions. Latexstabilizing surfactants function to prevent latex coagulation, and thosewhich are particularly suitable for use in accordance with thisinvention are surfactants having the formula

R—Ph—O(OCH₂CH₂)_(m)OH

[0047] wherein R is an alkyl group having from about 5 to about 30carbon atoms, Ph is phenyl and m is an integer in the range of fromabout 5 to about 50. Additional particularly suitable surfactants havethe general formula

R₁(OR₂)_(n)SO₃X

[0048] wherein R₁ is selected from the group consisting of alkyl groupshaving from 1 to about 30 carbon atoms, cycloalkyl groups having 5 or 6carbon atoms, C₁- C₄ alkyl substituted cycloalkyl groups, phenyl, alkylsubstituted phenyl of the general formula (R₃)_(a)Ph— wherein Ph isphenyl, R₃ is an alkyl group having from 1 to about 18 carbon atoms anda is an integer of from 1 to 3, and phenyl-alkyl groups wherein thealkyl groups have from 1 to about 18 carbon atoms and the phenyl-alkylgroups have a total of from about 8 to about 28 carbon atoms. R₂ is asubstituted ethylene group of the formula —CH₂CH₂R₄ wherein R₄ isselected from hydrogen, methyl, ethyl or mixtures thereof, n is a numberfrom 0 to about 40 provided that when R₁ is phenyl or alkyl substitutedphenyl n is at least one, and X is any compatible cation.

[0049] A preferred surfactant in the above defined group is ethoxylatednonylphenyl containing in the range of from about 20 to about 30 molesof ethylene oxide. Another preferred surfactant in the group is a sodiumsalt having the general formula

R₅—Ph(OR6)_(o)SO₃X

[0050] wherein R₅ is an alkyl group having in the range of from 1 toabout 9 carbon atoms, R₆ is the group —CH₂CH₂—, o is an integer fromabout 10 to about 20 and X is a compatible cation. Yet another preferredsurfactant in the group is a sodium salt having the formula

R₇(OR₈)_(p)SO₃X

[0051] wherein R₇ is an alkyl group having in the range of from about 5to about 20 carbon atoms, R₈ is the group —CH₂CH₂—, p is an integer inthe range of from about 10 to about 40 and X is a compatible cation. Aparticularly preferred surfactant of this type is the sodium salt of asulfonated compound derived by reacting a C₁₂ to C₁₅ alcohol with about15 moles of ethylene oxide having the formula

H(CH₂)₁₂₋₁₅(CH₂CH₂O)₁₅SO₃Na

[0052] which is commercially available under the name “AVANEL S150™”from PPG Mazer, Mazer Chemicals, a Division of PPG Industries, Inc., ofGurnee, Ill.

[0053] Of the various latex stabilizing surfactants described abovewhich can be used, ethoxylated nonylphenol containing in the range offrom about 15 to about 40 moles of ethylene oxide and the sodium salt ofa sulfonated and ethoxylated compound having the formulaH(CH₂)₁₂₋₁₅(CH₂CH₂O)₁₅SO₃Na are preferred, with the latter being themost preferred.

[0054] When a latex stabilizing surfactant is included in the sealingcompositions of this invention, it is added in an amount up to about 35%by weight of the aqueous rubber latex included therein, i.e., in anamount in the range of from about 3% to about 6% by weight of thecompositions.

[0055] The third sealing composition described above, i.e., thecomposition containing a water swellable clay, a silane coupling agent,an epoxy resin and a hardening agent, can include one or more waterswellable clays including, but not limited to sodium bentonite,attapulgite, fuller's earth and sepiolite. Of these, bentonite ispreferred. The water swellable clay utilized is included in the sealingcomposition in an amount in the range of from about 10% to about 50% byweight of the composition.

[0056] The silane coupling agent included in the sealing compositionstrengthens the bond between subterranean formation surfaces and thehardened sealing composition.

[0057] While various silane compounds can be used, particularly suitablesilanes include N-2-(aminoethyl)-3-aminopropyltrimethoxysilane,aminopropyltriethoxysilane and 3-5 aminopropyltrimethoxysilane. Ofthese, N-2-(aminoethyl)-3-aminopropyltrimethoxv-silane is preferredwhich is commercially available under the tradename “SILANE A1120™” fromthe Whitco Corporation of Greenwich, Conn. The silane coupling agent isincluded in the sealing composition in an amount in the range of fromabout 0. 1% to about 5% by weight of the composition.

[0058] A variety of other components can be included in the sealingcompositions of this invention to provide particular properties requiredfor specific applications. For example, in the first and second sealingcompositions described above, the polymerized rubber can be vulcanized(crosslinked) by including a vulcanizing agent such as sulfur therein.Inert fillers can be included in the sealing compositions to increasethe downhole yield of the compositions and/or provide additionalhardness to the sealing compositions. Examples of such fillers aresilica flour, silica fume, pozzolans and the like. In applications wherea well bore is to be plugged and not subsequently drilled out, cementsuch as Portland cement can be added to the sealing compositions.Another component which can be added to the sealing compositions is adeemulsifying surfactant which functions to break water in oil emulsiondrilling fluids. While such an emulsion breaker is generally not neededin that when a sealing composition of this invention contacts aninverted emulsion drilling fluid, it functions itself to break thedrilling fluid into its oil and water components. Some invertedemulsions utilizing synthetic oils are very difficult to break and thepresence of a separate deemulsifying agent in the sealing composition ishelpful.

[0059] The sealing compositions can also be foamed with nitrogen orother suitable gas in the presence of a foaming agent and foamstabilizer for reducing the densities of the compositions, preventingfluid loss and aiding in the diversion of the compositions into zones tobe sealed. Suitable foaming agents which can be used are one or moresulfonated linear alcohols or a cocoamidobetaine. A suitable foamstabilizer is comprised of a mixture of methoxypolyethylene glycols. Asis well understood by those skilled in the art, a variety of otherfoaming agents and foam stabilizers can also be used.

[0060] A preferred sealing composition of this invention is comprised ofwater present in an amount of from about 30% to about 42% by weight ofthe composition, an aqueous 25%:75% by weight styrene/butadiene latexwhich contains water in an amount of about 50% by weight of the latexpresent in an amount in the range of from about 10% to about 12% byweight of the composition, a latex stabilizer comprised of the sodiumsalt of a sulfonated and ethoxylated compound having the formulaH(CH₂)₁₂₋₁₅(CH₂CH₂O)₁₅SO₃Na present in an amount in the range of fromabout 3% to about 6% by weight of the composition, an alkyl quaternaryammonium bentonite clay present in an amount in the range of from about15% to about 19% by weight of the composition, sodium carbonate presentin an amount in the range of from about 3.3% to about 3.7% by weight ofthe composition, an epoxy resin comprised of a condensation product ofepichlorohydrin and bisphenol A present in an amount in the range offrom about 5% to about 20% by weight of the composition, an epoxy resinhardening agent comprised of an aliphatic or aromatic amine present inan amount in the range of from about 10% to about 20% by weight of thecomposition, welan gum biopolymer present in an amount in the range offrom about 0.1% to about 0.2% by weight of the composition, a dispersingagent comprised of the condensation reaction product of acetone,formaldehyde and sodium sulfite present in an amount in the range offrom about 0.4% to about 0.47% by weight of the composition and adefoaming agent comprised of polymethylsiloxane present in an amount inthe range of from about 0.8% to about 1.2% by weight of the composition.

[0061] Another preferred sealing composition of this invention iscomprised of an aqueous 25%:75% by weight styrene/butadiene latex whichcontains water in an amount of about 50% by weight of the latex presentin an amount in the range of from about 40% to about 50% by weight ofthe sealing composition, a latex stabilizing surfactant comprised of thesodium salt of a sulfonated and ethoxylated compound having the formulaH(CH₂)₁₂₋₁₅(CH₂CH₂)₁₅SO₃Na present in an amount in the range of fromabout 5% to about 15% by weight of the sealing composition, an epoxyresin comprised of a condensation product of epichlorohydrin andbisphenol A, an epoxidized bisphenol A novolac resin or one or moreepoxide containing liquids selected from the group of the diglycidylether of 1,4-butanediol, the diglycidyl ether of neopentylglycol or thediglycidyl ether of cyclohexanedimethanol present in an amount in therange of from about 40% to about 50% by weight of the sealingcomposition and an epoxy hardening agent comprised of an aliphatic oraromatic amine present in an amount in the range of from about 5% toabout 30% by weight of the sealing composition.

[0062] Yet another preferred sealing composition is comprised of a waterswellable clay comprised of sodium bentonite present in an amount in therange of from about 20% to about 50% by weight of the sealingcomposition, a silane coupling agent comprised ofN-2-(aminoethyl)-3-aminopropyltrimethoxysilane present in an amount inthe range of from about 0.1% to about 5% by weight of the sealingcomposition, an epoxy resin comprised of a condensation product ofepichlorohydrin and bisphenol A, one or more epoxide containing liquidsselected from the group of the diglycidyl ether of 1,4-butanediol, thediglycidyl ether of neopentylglycol or the diglycidyl ether ofcyclohexanedimethanol present in an amount in the range of from about40% to about 50% by weight of the sealing composition and an epoxidehardening agent comprised of an aliphatic or aromatic amine present inan amount in the range of from about 5% to about 30% by weight of thesealing composition.

[0063] The sealing compositions of this invention can be prepared inaccordance with any of the well known mixing techniques so long as thelatex and latex stabilizing surfactant (if used) are not directlyadmixed without prior dilution by other liquids. In a preferred method,water (if used) is first introduced into a blender. The defoamer andlatex stabilizing surfactant (if used) are then sequentially added withsuitable agitation to disperse the constituents. The epoxy resin, thehardening agent for the resin and other liquid additives are then addedfollowed by the dry solids. The mixture is agitated for a sufficientperiod of time to mix the components and form a pumpable non-foamedslurry. The aqueous rubber latex (if used) is added last and mixed withthe sealing composition just prior to pumping the composition.

[0064] The methods of sealing a subterranean zone penetrated by a wellbore using the sealing compositions described above basically comprisethe steps of preparing a sealing composition, introducing the sealingcomposition into the subterranean zone by way of the well bore, and thenallowing the sealing composition to harden into a firm but resilientsealing mass in the zone. Generally, the sealing composition is preparedin mixing apparatus on the surface and then pumped down the well boreinto the zone to be sealed at a high pressure whereby the viscous massformed in the well bore is squeezed into fractures and vugs. A fluidpressure above the fracture gradient can also be used in someapplications to fracture the zone being sealed and force the sealingcomposition into the fractures thereby increasing the overall strengthof the zone.

[0065] The methods of sealing a subterranean zone using the second andthird sealing compositions described above are carried out so that thesealing compositions do not contact the oil or water based drillingfluids in the well bore until they reach the open hole lost circulationzone of the well bore. That is, when the second sealing compositiondescribed above is used, i.e., a sealing composition comprised of anaqueous rubber latex, a latex stabilizing surfactant, an epoxy resin orone or more epoxide containing liquids and a hardening agent, thefollowing procedure is utilized.

[0066] With the well bore filled with oil or water based drilling fluid,the open bottom end of the drill string or a work string (hereinafterreferred to as the “pipe string”) is positioned about one hundred feetabove the lost circulation zone. A spacer of water is pumped into thepipe string followed by the sealing composition which is followed byanother spacer of water. When the first spacer reaches the bottom of thepipe string, the pumping of the sealing composition is stopped and theoil or water based drilling fluid is pumped through the annulus at arate approximately twice the rate at which the sealing composition wasbeing pumped. When the drilling fluid pumping pressure increases, thepumping of the sealing composition is continued until the sealingcomposition has been pumped into the open hole zone of the well bore.The pipe string is then moved upwardly away from the lost circulationzone. The pumping of the drilling fluid is continued until the fractureinitiation pressure is reached. Drilling fluid is then circulatedthrough the pipe string to remove sealing composition from the insidesurfaces thereof, and the sealing composition is allowed to harden.Thereafter, the well bore is drilled through the sealing composition andnormal drilling is continued.

[0067] When the third sealing composition is used, i.e., a sealingcomposition comprised of a water swellable clay, a silane couplingagent, an epoxy resin or one or more epoxide containing liquids and ahardening agent, the procedure followed is the same as above except thatthe well is full of water based drilling fluid and oil spacers areutilized instead of water spacers.

[0068] As previously mentioned, the sealing compositions of thisinvention enter the weakest portions of the zone first followed by otherportions including those where fluids crossflow through the well bore orblow-out into the well bore. The sealing compositions stop drillingfluid losses and allow high drilling fluid densities to be utilized whenneeded while drilling ahead. Once the sealing compositions have beenplaced and form a firmer but resilient sealing mass in a subterraneanzone, they increase the fracture gradient to a higher level that caneliminate the need for intermediate casing, drilling liners and thelike. Because the sealing compositions readily divert to other weakzones in the well bore, the integrity of the entire well bore isimproved by the sealing compositions. In some applications it may benecessary to pump an activator fluid, e.g., an aqueous calcium chloridesolution and/or oil ahead of the sealing composition into the zone to besealed so that the sealing composition will react to form a viscous massprior to being squeezed into the zone.

[0069] In order to further illustrate the compositions and methods ofthe present invention, the following examples are given.

EXAMPLE 1

[0070] A sealing composition of this invention (the first sealingcomposition described above) was prepared comprised of water present inan amount of about 3.32% by weight of the composition, an aqueous25%:75% by weight styrene/butadiene latex which contained water in anamount of about 50% by weight of the latex present in an amount of about3.32% by weight of the composition, a latex stabilizer comprised of thesodium salt of a sulfonated and ethoxylated compound having the formulaH(CH₂)₁₂₋₁₅(CH₂CH₂O)₁₅SO₃Na present in an amount of about 0.67% byweight of the composition, an alkyl quaternary ammonium bentonite claypresent in an amount of about 3.6% by weight of the composition, sodiumcarbonate present in an amount of about 0.36% by weight of thecomposition, welan gum biopolymer present in an amount of about 0.03% byweight of the composition, a dispersing agent comprised of thecondensation reaction product of acetone, formaldehyde and sodiumsulfite present in an amount of about 0.05% by weight of the compositionand a defoaming agent comprised of polymethylsiloxane present in anamount of about 0.002% by weight of the composition. Three differentepoxy resins identified in the Table below were combined with portionsof the above described compositions along with a diethyltoluenediamineepoxy resin hardening agent in the amounts shown in the Table below. Thethree compositions were each mixed at 140° F. for the time required forthem to reach a viscosity of 100 B_(c). Portions of the compositionswere cured at 140° F. for 72 hours and then tested for compressivestrength. Additional portions of the composition were mixed with equalvolumes of a water-in-oil emulsion and the resulting mixtures were curedat 140° F. for 72 hours after which their compressive strengths weredetermined. The results of these tests are shown in the Table below.TABLE Time Amount of Amount of Required Compressive Strengths EpoxyResin Hardening Agent at 140° F. After 72 hrs in the in the to Reach 100at 140° F. psi Composition, % Composition, % B_(c) Without WithComposition by weight of by weight of Viscosity, Water-in-oilWater-in-oil Tested the Composition the Composition hr:min EmulsionEmulsion A¹ 58 12.2 4:00 40⁴ 12⁴ B² 58 14.3 3:50 27⁴ 10⁴ C³ 58 12.2 3:507⁴ 5⁴

[0071] As can be seen in the Table above, the compositions of thepresent invention form firm resilient sealing masses which retain theirshape and have good compressive strengths.

EXAMPLE 2

[0072] Another sealing composition of this invention (the secondcomposition described above) was prepared and mixed with an equalportion of a synthetic oil based drilling fluid. The resulting mixturewas comprised of an aqueous 25%:75% by weight styrene/butadiene latexwhich contained water in an amount of about 50% by weight of the latexpresent in the mixture in an amount of about 20.8% by weight of themixture, a latex stabilizer comprised of the sodium salt of a sulfonatedand ethoxylated compound having the formula H(CH₂)₁₂₋₁₅(CH₂CH₂O)₁₅SO₃Napresent in an amount of about 4.2% by weight of the mixture, an epoxyresin comprised of an aqueous dispersion of the condensation product ofepichlorohydrin and bisphenol A (“EPI-REZ®-3510-W-60”) present in anamount of about 20% by weight of the mixture, an epoxy resin hardeningagent comprised of diethyltoluenediamine present in an amount of about5% by weight of the mixture and the synthetic oil based drilling fluidpresent in an amount of about 50% by weight of the mixture. A portion ofthe mixture was mixed at 140° F. for the time required for it to reach aviscosity of 100B_(c). Another portion of the mixture was then cured at140° F. for 72 hours after which its compressive strength wasdetermined.

[0073] The time required to reach 100 B_(c) was 4 hrs:25 min. and thecompressive strength of the mixture was 52 psi.

EXAMPLE 3

[0074] The third sealing composition described above was prepared andmixed with an equal portion of a water based drilling fluid. Theresulting mixture was comprised of sodium bentonite present in themixture in an amount of 6% by weight of the mixture, a silane couplingagent, i.e., N-2-(aminoethyl)-3-aminopropyltrimethoxysilane present inan amount of 0.5% by weight of the mixture, an epoxy resin comprised ofan aqueous dispersion of the condensation product of epichlorohydrin andbisphenol A present in an amount of about 34% by weight of the mixture,an epoxy resin hardening agent comprised of diethyltoluenediaminepresent in an amount of about 9.5% by weight of the mixture and thewater based drilling fluid present in an amount of about 50% by weightof the mixture.

[0075] The time required for the mixture to reach a viscosity of 100B_(c) was 3 hrs:30 min. and the compressive strength of the mixture was38 psi.

[0076] Thus, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosewhich are inherent therein. While numerous changes may be made by thoseskilled in the art, such changes are encompassed within the spirit ofthis invention as defined by the appended claims.

What is claimed is:
 1. An improved sealing composition for sealing asubterranean zone penetrated by a well bore comprising: an aqueousrubber latex; a latex stabilizing surfactant; an epoxy resin; and ahardening agent for said epoxy resin.
 2. The composition of claim 1wherein said aqueous rubber latex is present in an amount in the rangeof from about 30% to about 70% by weight of said composition.
 3. Thecomposition of claim 2 wherein said aqueous rubber latex is an aqueousstyrene-butadiene latex.
 4. The composition of claim 2 wherein saidaqueous rubber latex is an aqueous 25%:75% by weight styrene-butadienelatex which contains water in an amount of about 50% by weight of saidlatex.
 5. The composition of claim 1 wherein said latex stabilizingsurfactant is present in an amount in the range of from about 3% toabout 6% by weight of said composition.
 6. The composition of claim 5wherein said latex stabilizing surfactant is selected from the groupconsisting of nonylphenol ethoxylated with in the range of from about 15to about 40 moles of ethylene oxide and the sodium salt of a sulfonatedand ethoxylated compound having the formula H(CH₂)₁₂₋₁₅(CH₂CH₂O)₁₅SO₃Na.7. The composition of claim 1 wherein said epoxy resin is present in anamount in the range of from about 30% to about 70% by weight of saidcomposition.
 8. The composition of claim 7 wherein said epoxy resin isselected from the group consisting of a condensation product ofepichlorohydrin and bisphenol A, an epoxidized bisphenol A novolacresin, the diglycidyl ether of 1,4-butanediol, the diglycidyl ether ofneopentyl glycol, the diglycidyl ether of cyclohexanedimethanol andmixtures thereof.
 9. The composition of claim 7 wherein said epoxy resinis comprised of the condensation product of epichlorohydrin andbisphenol A.
 10. The composition of claim 1 wherein said hardening agentis present in an amount in the range of from about 5% to about 30% byweight of said composition.
 11. The composition of claim 10 wherein saidhardening agent is selected from the group consisting of aliphaticamines, aromatic amines, carboxylic acid anhydrides and mixturesthereof.
 12. The composition of claim 10 wherein said hardening agent isselected from the group of isophoronediamine, diethyltoluenediamine,tris(dimethylaminoethylphenol) and mixtures thereof.
 13. An improvedsealing composition for sealing a subterranean zone penetrated by a wellbore comprising: an aqueous 25%:75% by weight styrene/butadiene latexwhich contains water in an amount of 50% by weight of the latex presentin an amount in the range of from about 40% to about 50% by weight ofsaid composition; a latex stabilizing surfactant comprised of the sodiumsalt of a sulfonated and ethoxylated compound having the formulaH(CH₂)₁₂₋₁₅(CH₂CH₂O)₁₅SO₃Na present in an amount in the range of fromabout 5% to about 15% by weight of said composition; an epoxy resinselected from the group consisting of a condensation product ofepichlorohydrin and bisphenol A, an epoxidized bisphenol A novolacresin. the diglycidyl ether of 1,4-butanediol, the diglycidyl ether ofneopentyl glycol, the diglycidyl ether of cyclohexanedimethanol andmixtures thereof present in an amount in the range of from about 40% toabout 50% by weight of said composition; and an epoxy hardening agentselected from the group consisting of isophoronediamine,diethyltoluenediamine, tris(dimethylaminoethylphenol) and mixturesthereof present in an amount in the range of from about 5% to about 30%by weight of said composition.
 14. An improved sealing composition forsealing a subterranean zone penetrated by a well bore comprising: awater swellable clay; a silane coupling agent; an epoxy resin; and ahardening agent for said epoxy resin.
 15. The composition of claim 14wherein said water swellable clay is present in an amount in the rangeof from about 20% to about 50% by weight of said composition.
 16. Thecomposition of claim 15 wherein said water swellable clay is selectedfrom the group consisting of sodium bentonite, attapulgite, fuller'searth and sepiolite.
 17. The composition of claim 15 wherein said waterswellable clay is sodium bentonite.
 18. The composition of claim 14wherein said silane coupling agent is present in an amount in the rangeof from about 0.1% to about 5% by weight of said composition.
 19. Thecomposition of claim 18 wherein said silane coupling agent is selectedfrom the group consisting ofN-2-(aminoethyl)-3-amninopropyltrimethoxysilane,aminopropyltriethoxysilane and 3-amninopropyltrimethoxysilane.
 20. Thecomposition of claim 18 wherein said silane coupling agent isN-2-(aminoethyl)-3-aminopropyltrimethoxysilane.
 21. The composition ofclaim 14 wherein said epoxy resin is present in an amount in the rangeof from about 30% to about 70% by weight of said composition.
 22. Thecomposition of claim 21 wherein said epoxy resin is selected from thegroup consisting of a condensation product of epichlorohydrin andbisphenol A, an epoxidized bisphenol A novolac resin, the diglycidylether of 1,4-butanediol, the diglycidyl ether of neopentyl glycol, thediglycidyl ether of cyclohexanedimethanol and mixtures thereof.
 23. Thecomposition of claim 21 wherein said epoxy resin is comprised of thecondensation product of epichlorohydrin and bisphenol A.
 24. Thecomposition of claim 14 wherein said hardening agent is present in anamount in the range of from about 5% to about 30% by weight of saidcomposition.
 25. The composition of claim 24 wherein said hardeningagent is selected from the group consisting of aliphatic amines,aromatic amines, carboxylic acid anhydrides and mixtures thereof. 26.The composition of claim 24 wherein said hardening agent is selectedfrom the group of isophoronediamine, diethyltoluenediamine,tris(dimethylaminoethylphenol) and mixtures thereof.
 27. An improvedsealing composition for sealing a subterranean zone penetrated by a wellbore comprising: a water swellable clay comprised of sodium bentonitepresent in an amount in the range of from about 20% to about 50% byweight of said composition; a silane coupling agent comprised ofN-2-(aminoethyl)-3-aminopropyltrimethoxysilane present in an amount inthe range of from about 0.1% to about 5% by weight of said composition;an epoxy resin selected from the group consisting of a condensationproduct of epichlorohydrin and bisphenol A, an epoxidized bisphenol Anovolac resin, the diglycidyl ether of 1,4-butanediol, the diglycidylether of neopentyl glycol, the diglycidyl ether of cyclohexanedimethanoland mixtures thereof present in an amount in the range of from about 40%to about 50% by weight of said composition; and an epoxy hardening agentselected from the group consisting of isophoronediamine,diethyltoluenediamine and tris(dimethylaminoethylphenol) and mixturesthereof present in an amount in the range of from about 5% to about 30%by weight of said composition.
 28. An improved method of sealing asubterranean zone penetrated by a well bore comprising the steps of:preparing a subterranean zone sealing composition comprising an aqueousrubber latex, a latex stabilizing surfactant, an epoxy resin and ahardening agent for said epoxy resin; introducing said sealingcomposition into said zone by way of said well bore; and allowing saidsealing composition to harden into a firm but resilient sealing mass insaid zone.
 29. The method of claim 28 wherein said aqueous rubber latexis an aqueous styrene/butadiene latex and is present in an amount in therange of from about 30% to about 70% by weight of said composition. 30.The method of claim 28 wherein said latex stabilizing surfactant isselected from the group consisting of nonylphenol ethoxylated with inthe range of from about 15 to about 40 moles of ethylene oxide and thesodium salt of a sulfonated and ethoxylated compound having the formulaH(CH₂)12-15(CH₂CH₂O)₁₅SO₃Na present in an amount in the range of fromabout 3% to about 6% by weight of said composition.
 31. The method ofclaim 28 wherein said epoxy resin is selected from the group consistingof a condensation product of epichlorohydrin and bisphenol A, anepoxidized bisphenol A novolac resin, the diglycidyl ether of1,4-butanediol, the diglycidyl ether of neopentyl glycol, the diglycidylether of cyclohexanedimethanol and mixtures thereof, and said epoxyresin is present in an amount in the range of from about 30% to about70% by weight of said composition.
 32. The method of claim 28 whereinsaid hardening agent selected from the group consisting of aliphaticamines, aromatic amines and carboxylic acid anhydrides and is present inan amount in the range of from about 5% to about 30% by weight of saidcomposition.
 33. An improved method of sealing a subterranean zonepenetrated by a well bore comprising the steps of: preparing asubterranean zone sealing composition comprising a water swellable clay,a silane coupling agent, an epoxy resin and a hardening agent for saidepoxy resin; introducing said sealing composition into said zone by wayof said well bore; and allowing said sealing composition to harden intoa firm but resilient sealing mass in said zone.
 34. The method of claim33 wherein said water swellable clay is selected from the groupconsisting of sodium bentonite, attapulgite, fuller's earth andsepiolite and is present in an amount in the range of from about 20% toabout 50% by weight of said composition.
 35. The method of claim 33wherein said silane coupling agent is selected from the group consistingof N-2-(aminoethyl)-3-aminopropyltrimethoxysilane,aminopropyltrimethoxysilane and 3-aminopropyltrimethoxysilane and ispresent in an amount in the range of from about 0.1% to about 5% byweight of said composition.
 36. The method of claim 33 wherein saidepoxy resin is selected from the group of a condensation product ofepichlorohydrin and bisphenol A, an epoxidized bisphenol A novolacresin, the diglycidyl ether of 1,4-butanediol, the diglycidyl ether ofneopentyl glycol, the diglycidyl ether of cyclohexanedimethanol andmixtures thereof, and said epoxy resin is present in an amount in therange of from about 30% to about 70% by weight of said composition. 37.The method of claim 33 wherein said hardening agent is selected from thegroup consisting of aliphatic amines, aromatic amines and carboxylicacid anhydrides and is present in an amount in the range of from about3% to about 6% by weight of said composition.